NEUFELD'S QUELLING REACTION 225 



NEUROFIBRILS 



this substance as Nissl techniques even 

 though resemblance to the original 

 method is lacking. 



2. The original Golgi method for the 

 external form of nerve cells depends 

 upon preliminary mordanting of tissue 

 in potassium bichromate solutions, fol- 

 lowed by immersion in weak aqueous 

 silver nitrate, and the cutting of thick 

 sections in which occasional nerve cells 

 and processes are outlined with startling 

 clarity by the black deposit of silver 

 chromate. Cajal modified and speeded 

 up the technique by addition of osmic 

 acid to the bichromate solution (see 

 Golgi Method, quick). But the most 

 used modification is the Golgi Cox 

 technique. 



3. The original Weigert method for 

 myelin sheaths of nerve fibers depended 

 likewise upon preliminary mordanting 

 in bichromate and the formation of 

 hematoxylin "lakes" when the sections 

 were later stained with hematoxylin. 

 Its most important modification is 

 known as Weigert-Pal. The Marchi 

 method, as modified by Swank and 

 Davenport is based on similar mordant- 

 ing with bichromate after which they 

 are treated with osmic acid and was 

 designed to reveal degenerated myelin 

 sheaths the lipids of which are unaf- 

 fected by the mordanting and are 

 blackened while those of the normal 

 sheaths are not. 



4. Cajal and Bielchowsky introduced 

 valuable methods for axones, neuro- 

 fibrils, and nerve endings including 

 synapses. Both techniques as applied 

 to blocks of tissue depend on preliminary 

 "silvering" with weak silver nitrate 

 solution but in those of the former the 

 silver is reduced by a photographic 

 developer generally hydroquinone or 

 pyrogallic acid; while in those of the 

 latter the tissues are first brought into 

 an ammoniacal silver solution and then 

 reduced in formalin. The most useful 

 modification is the Bodian Method 

 of activated protargol. See its evolu- 

 tion under Silver Methods which are 

 of assistance in the study of many 

 other tissues of the body as well as the 

 nervous system. 



5. Weigert 's neuroglia stain was also 

 a classic, likewise Cajal's gold chloride 

 and sublimate method (1913) which 

 was soon followed by Hortega's car- 

 bonate silver method (1917). See recent 

 techniques under Neuroglia. 



There are still other techniques to 

 choose from which are not so directly 

 developments of the neurological 

 classics. Nerve cells are closely mixed 

 with fibers . To isolate them sufficiently 



for direct study at high magnification 

 in approximately isotonic media in- 

 volves considerable injury and they 

 cannot be held under observation for 

 long periods because their death ensues 

 fairly quickly. Spinal ganglion cells 

 are the easiest studied. The Macera- 

 tion technique is not much used for the 

 nervous system but Addison (McClung, 

 p. 439) states that, if pieces of the 

 anterior horn of the spinal cord are 

 treated with Gage's dissociator (0.2% 

 formalin in physiological saline) for 

 2-3 days, the nerve cells can easily be 

 dissected out under a binocular micro- 

 scope, stained and examined more or 

 less as units. Tissue Culture of nerve 

 cells of the adult is not feasible because 

 they are fixed postmitotics (having 

 permanently lost the power of multi- 

 plication) ; but culture of young tissues 

 provides interesting results (Levi, G., 

 Arch, de Biol., 1941, 52, 1-278, profusely 

 illustrated). Nerve Fibers are more 

 easily isolated and their investigation 

 in the fresh state is very profitable. 

 The histological localization of Cho- 

 linesterase is now feasible. The meas- 

 urement of oxidative metabolism in dif- 

 ferent parts of the nerve cell by 

 reduction of ferric chloride (Gerard, 

 R. W., Assoc, for Res. in Nerv. & Ment. 

 Dis., Baltimore, Williams & Wilkins, 

 1938, 18, 316-345) can probably be tied 

 up with localization of Oxidases and 

 Peroxidases. Marinesco (G., Arch. 

 Suisse de Neurol, et de Psych., 1924, 

 15, 1-24) has published repeatedly on 

 these enzymes in nerve cells. Methods 

 for Pigments and Lipids can easily be 

 applied to the nervous system. For 

 microincineration of nerve cells and 

 fibers see Scott, G. H., Proc. Soc. Exp. 

 Biol. & Med., 1940, 44, 397-398. If it is 

 desired to demonstrate mitochondria 

 the Anilin-Fuchsin Methyl Green 

 method is suggested after fixation by 

 vascular perfusion plus immersion. See 

 in addition to above headings : Auer- 

 bach's Plexus, Axis Cylinders, Boutons 

 Terminaux, Centrosomes, Cresyl Violet, 

 Golgi Apparatus, Microglia, Motor 

 End Plates, Nerve Endings, Neuro- 

 fibrils, Neurosecretory Cells, Oligo- 

 dendroglia. 



Neufeld's Quelling Reaction. This is a 

 microscopically demonstrable swelling 

 of the capsules of pneumococei which is 

 of distinct value in typing (L. W. Parr, 

 in Simmons and Gentzkow, p. 42fi). 



Neumann's Crystals, see Charcot-Leyden. 



Neurites, see Nerve Fibers. 



Neurofibrils. These delicate fibrils and 

 networks can be demonstrated with 

 difficulty mainly by methods of silver 



